1. **Signal Layers**
Altium Designer allows for up to 32 signal layers in a multilayer PCB, including the Top Layer, Bottom Layer, and Mid-Layers. These layers are interconnected using various via types: through vias, blind vias, and buried vias.
– **Top Layer**
Also known as the component layer, the Top Layer is primarily used for component placement. In both double-layer and multilayer boards, this layer is also used for routing signal traces or adding copper areas to manage heat dissipation or EMI shielding.
– **Bottom Layer**
Often referred to as the soldering layer, the Bottom Layer is mainly used for routing signal traces and providing space for solder pads. In double-layer and multilayer boards, it can also be used for component placement, especially for surface-mount devices (SMDs).
– **Mid-Layers**
Mid-layers can be used to create up to 30 additional signal layers in a multilayer PCB. These layers are dedicated to routing signal traces but do not include power or ground connections. Mid-layers help in managing the complexity of high-density signal routing, reducing the overall PCB size and optimizing performance.
2. **Internal Planes**
Internal planes refer to dedicated layers that carry power and ground traces in a multilayer PCB. These planes are crucial for minimizing signal noise and providing stable power distribution. Internal planes are typically used in conjunction with signal layers to form a balanced structure that enhances the electrical performance of the board.
### 1. Inner Electric Layers
The term “inner electric layer” typically refers to the internal conductive layers in a **multilayer PCB**. These layers are found between the signal layers and are crucial for creating electrical connections within the board. The total number of layers in a PCB is usually counted as the sum of the signal layers and inner electric layers. Similar to signal layers, these inner layers can be interconnected using **through holes**, **blind holes**, or **buried holes**, allowing for complex routing of signals and power throughout the board.
### 2. Silkscreen Layers
A **PCB silkscreen layer** can include up to two separate layers: the **Top Silkscreen Layer (Top Overlay)** and the **Bottom Silkscreen Layer (Bottom Overlay)**. These layers are typically printed in white and serve as a means of labeling and annotating the PCB. The key functions of the silkscreen layers are to provide information such as component outlines, designators, and other identification marks, aiding in component placement and circuit inspection during both assembly and testing.
#### (1) Top Overlay
The **Top Overlay** layer contains markings that indicate the outlines and labels for components on the top side of the PCB. This includes component designators (such as R1, C2), nominal values, and other textual annotations that guide the assembly process.
#### (2) Bottom Overlay
The **Bottom Overlay** layer serves the same purpose as the top silkscreen but applies to the bottom side of the board. In many designs, the bottom silkscreen layer mirrors the top one. If all necessary information is already included in the top layer, the bottom layer may be left empty, or only essential annotations are placed.
### 3. Mechanical Layers
The **mechanical layers** are primarily used to store information related to the manufacturing and assembly of the PCB, such as board dimensions, drill hole sizes, and assembly guidelines. These layers are critical for defining the physical characteristics of the PCB and providing the manufacturer with the details necessary for fabrication and assembly.
#### Key Mechanical Layers:
– **Mechanical 1**: Often used to define the **mechanical outline** or the overall shape of the PCB. It is commonly referred to as the “shape layer.”
– **Mechanical 2**: Contains information on **process requirements**, including size, layer count, and material specifications.
– **Mechanical 13 & Mechanical 15**: These layers include the **3D component body information** and are used to represent the physical size and shape of components, typically from an **ETM library**. These layers are hidden by default to simplify the view but can be displayed when needed.
– **Mechanical 16**: This layer contains the **footprint information** of components from the ETM library and can help estimate the overall size of the PCB early in the design phase. Like Mechanical 13 & 15, it is hidden by default to maintain clarity in the design.
### 4. Mask Layers
In **Altium Designer**, there are two main types of **mask layers**: the **Solder Mask** and the **Paste Mask**. These layers have specific functions related to the protection and preparation of the PCB surface.
– **Solder Mask**: The solder mask is used to cover areas of the PCB where soldering is not required, helping to prevent unintended solder bridges during assembly. Both the top and bottom layers of the PCB will typically have solder mask applied.
– **Paste Mask**: The paste mask is specifically used to define where solder paste should be applied during the SMT (Surface Mount Technology) assembly process. Like the solder mask, paste masks are defined for both the top and bottom sides of the PCB, although they are not always visible by default in design layouts.
